The present invention relates to an electronic device for high frequency signals in which, as an insulating layer, a low dielectric loss tangent resin composition is used for coping with high frequency signals.
In recent years, signal bands of information communication equipment, such as a PHS or a portable telephone, and the CPU clock times of computers have reached GHz bands, and the working frequency has become higher. The dielectric loss of electric signals is in proportion to the product of the square root of a specific dielectric constant, the dielectric loss tangent of an insulator forming the circuit and the frequency of the signals being used. Accordingly, the dielectric loss increases as the frequency of the signals being used increases. Since an increase in the dielectric loss attenuates the electric signals so as to deteriorate the reliability of the signals, it is necessary to select the insulating material from materials of low dielectric constant and low dielectric loss tangent to suppress such a loss. To lower the dielectric constant and the dielectric loss tangent of an insulator, it is effective to remove polar groups in the molecular structure, and fluoro resins, curable polyolefins, cyanate ester type resins, curable polyphenylene oxides, allyl modified polyphenylene ethers, polyvinyl benzyl ether, or divinyl benzene or divinyl naphthalene-modified polyether imides have been proposed.
Fluoro resins typically represented by polytetrafluoroethylene (PTFE) have a low dielectric constant and low dielectric loss tangent and are used for insulating layers of various electronic devices that are designed to handle high frequency signals. On the other hand, various non-fluoro resins of low dielectric constant and low dielectric loss tangent, which are soluble to organic solvents and are handled easily, have also been studied. They include various examples, for example, dienic polymers, such as polybutadiene impregnated into glass cloth and cured by peroxides, as disclosed in Japanese Patent Laid-open 8-208856; cyclic polyolefins formed by introducing epoxy groups into norbornene series addition type polymers, as disclosed in Japanese Patent Laid-open 10-158337; cyanate esters, dienic polymers and epoxy resins heated into B stage, as disclosed in Japanese Patent Laid-open 11-124491; modified resins including polyphenylene oxides, dienic polymers and triallyl isocyanates, as disclosed in Japanese Patent Laid-open 9-118759; resin compositions comprising, for example, allylated polyphenylene ethers and triallylisocyanates, as disclosed in Japanese Patent Laid-open 9-246429; polyetherimides alloyed with styrene, divinyl benzene or divinyl naphthalene, as disclosed in Japanese Patent Laid-open 5-156159, and resin compositions comprising thermosetting resins having vinyl benzyl ether groups and various kinds of additives, as disclosed in Japanese Patent Laid-open 5-78552 and 2001-247733. Since low dielectric constant, low dielectric loss tangent resin compositions have to endure electric device production steps, including steps such as solder reflow and gold wire bonding, each of them is designed as a thermosetting resin.
An insulating layer using a low dielectric constant, low dielectric loss tangent resin composition has a characteristic that is capable of decreasing the dielectric loss of high frequency signals, as well as being capable of attaining a high speed transmission and high characteristic impedance.
On the other hand, the insulating layer of high frequency circuits requires formation of delay circuits, impedance matching of wiring substrates in low impedance circuits, refinement of the wiring pattern, constitution of composite circuit incorporating capacitors in the substrate per se and the like, and the insulating layer requires a higher dielectric constant in some cases. Therefore, various proposals have been made, for example, to provide an electronic device using a high dielectric and low dielectric loss tangent insulating layer, as described in Japanese Laid-open No. 2000-91717, and electronic devices formed by compositing a high dielectric constant layer, and a low dielectric constant layer as described in Japanese Patent Laid-open Nos. 2001-247733 and 2001-345212. The high dielectric constant and low dielectric loss tangent insulating film is prepared by dispersing a high dielectric insulating material, such as a ceramic powder or metal powder applied with insulation treatment, in the low dielectric constant and low dielectric loss tangent insulating layer described above.
As described above, in an electronic device for high frequency signals, it is necessary that the dielectric constant of the insulating layer thereof be controlled depending on the property of the circuit to be formed. However, lowering of the dielectric loss tangent of the insulating layer is essential in any case in order to decrease the dielectric loss.